This invention relates to a method for producing a color filter and more particularly to a color filter advantageously employed as a color liquid crystal display device.
Among the currently employed methods for preparing a color filter, there are a dyeing method consisting in dyeing a transparent substrate with a binder containing dyes and pigments, a printing method and a pigment dispersion method.
Since the dyeing method consists in selectively forming a thin resin film on a substrate with dyes, a resist printing process and a photolithographic process need to be performed each time the color is changed. Although resist printing is unnecessary with the printing method, there is a limit to the refinement, of color patterns and, the larger is the number of colors, the printing position becomes the worse. Although the fine color pattern is possible with the pigment dispersion method, a high precision photolithographic process needs to be performed each time the color is changed, resulting in a complicated process.
For overcoming the deficiency, there is proposed in Japanese Laid-open Patent Application No. 59-114572 (1984) a method for producing a color filter by an electrodeposition coating method. With this method, a transparent electrode is prepared by patterning a transparent electrically conductive film deposited on the substrate, the substrate is immersed in a colored electrodeposition bath for forming a colored layer by electrodeposition, and electrical voltage is applied only to a portion of the patterned transparent electrode which is to be dyed in the same color. The substrate is then immersed in a colored electrodeposition bath for forming a different color layer by electrodeposition, and electric voltage is then applied only to a portion of the substrate which is to be dyed in a different color. However, it is necessary with this method to perform a high precision patterning of the transparent electrode, and to pay meticulous care during the subsequent process not to break the fine pattern, because otherwise the subsequent coloring process is rendered difficult. Besides, the patterned transparent electrode needs to be electrically continuous, even in fine pattern sections, so that limitations are imposed on the degree of freedom of the pattern shape.
In Japanese Laid-open Patent Application No. 63-210901 (1988), there is proposed a method consisting in forming colored layers by light exposure, development and electrodeposition, using a mask having patterns only in areas to be dyed in the same colors and a positive type photosensitive resin composition, and repeating the steps of light exposure, development and electrodeposition a desired number of times. This method is inferior in stability because it makes use of a compound containing unstable quinone diazido groups. Besides, if the quinone diazido compound is brought into contact with an aqueous alkali solution, the quinone diazido compound in the unexposed part is also reacted with an aqueous alkali solution so that photosensitivity is markedly changed to present difficulties in the subsequent light exposure and development steps.
In the aforementioned electrodeposition methods, the transparent electrode for forming colored layers thereon is also employed as an electrode for driving a liquid crystal display device. However, the colored layers formed on the transparent electrode are of dielectric nature so that voltage for driving the liquid crystal device is extremely high. Accordingly, on the practical application another transparent electrode for driving the liquid crystal device is further provided on the colored layers produced in accordance with the aforementioned methods so as to lower the driving voltage. In the meanwhile, as the transparent electrode employed in the aforementioned methods has light transmittance of 80 to 85%, the provision of two transparent electrodes poses another disadvantage in that light transmittance is lowered, leading to inferior performance of a colored display liquid crystal device. To solve such a problem, there is proposed in Japanese Laid-open Patent Application No. 1-22379 a method for forming colored layers on an original plate and transferring the colored layers on a transparent substrate. In the method, however, the transferring is performed for each color, thus necessitating high precision of alignment at respective transferring steps.
On the other hand, in order to meet the demand for high performance of the device provided with a color filter, it has been desired to improve contrast and to prevent color purity from being lowered. In order to solve this problem, a method of forming a non-light transmitting film in a region of the color filter defined between neighboring pixels has been proposed. For forming the non-light transmitting film, there are known a method comprising Forming pixels with alignment on a substrate on which a non-tight transmitting film pattern is formed previously, and a method comprising forming a non-light transmitting Film pattern with alignment on a substrate on which a pixel pattern is formed previously.
However, since it is necessary with these methods to effect an alignment operation between the pixel pattern and the non-light transmitting pattern, it is difficult with this precision to Form a pattern of non-light transmitting pattern of a coincident size free of the light transmitting sections between the pixel patterns. If overlapped portions are produced, step differences are produced on a color filter, so that it becomes difficult to produce a color filter excellent in planarity.
With any of the above methods, high precision processing is required for alignment so that it is difficult to cope with the demand for a larger work size, that is a larger picture size with reduced costs.
It is a principal object of the present invention to provide a method for producing a color filter which is not in need of high precision fine processing and which has a large degree of freedom in selecting any kind of patterns of the colored layers and non-light transmitting layers can be arrayed without gaps between the color filter pixels.
It is another object of the present invention to provide a method for preparing a color filter which can be adapted easily for larger picture size and which can be mass-produced easily.
It is a further object of the present invention to provide a method for producing a color filter which can lower the driving voltage without light transmission being lowered and which do not require an additional step of forming transparent electrodes.
It is a further object of the present invention to provide a method for producing a color filter having light-intercepting layers patterned with high precision.
The above and other objects of the invention will become apparent from the following description.
The present invention provides a method for producing a color filter comprising the steps of:
(A) forming a photosensitive coating film on at least a transparent electrically conductive layer of a substrate selected from the group consisting of a first substrate having both the transparent electrically conductive layer and a light-intercepting layer on its surface and a second substrate having the transparent electrically conductive layer on its outermost surface and a light-intercepting layer between the second substrate and the transparent electrically conductive layer and exposing the photosensitive coating film through a mask having patterns of at least three different degrees of light transmittances; and PA1 (B) developing and removing a photosensitive coating film region corresponding to a pattern selected from the group consisting of a pattern having smallest degree of light transmittance and a pattern having largest degree of light transmittance for exposing the transparent electrically conductive layer and electrodepositing a colored coating on the exposed transparent electrically conductive layer for forming a colored layer thereon, operation of developing and removing the photosensitive coating film and electrodepositing the colored coating being sequentially repeated for the respective patterns having different degrees of light transmittances where the sequence of repetition is selected from the group consisting of increasing light transmittance and decreasing light transmittance to form different colored layers, respectively.